Panels for vehicle applications, e.g., roof or door panels, are typically relatively thin in order to meet vehicle weight requirements and allow the panels to be shaped as may be desired for aesthetic and manufacturing reasons. The size and generally flat shape typical of these panels makes them susceptible to deformation. For example, sheetmetal panels may expand during vehicle body coating or painting operations under the application of heat. Additionally, the panels may experience deformation during vibration or other stresses imparted to the panel during vehicle operation.
Vehicle panels are therefore often reinforced using additional structural pieces such as a ribbed brace or reinforcement. Generally such braces are bonded directly to the panel with a very stiff structural reinforcing material. For example, adhesives may be applied to a brace or reinforcement in a bead extending along the brace. Since the brace is applied directly to the panel using the adhesive, variances in the thickness of the adhesive bead can create larger problems. Where an adhesive bead is too thin, a gap may be created between the brace and the panel and reduce structural support to the panel. Where an adhesive bead is too thick, excess adhesive may prevent proper coating of the vehicle body, e.g., in a electo-coating process.
Heat application processes typical of vehicle body construction, e.g., paint baking processes, may also cause difficulties for bonding of braces to a panel. For example, gaps between the brace and panel may be exacerbated where the panel and brace are formed of different materials having different thermal expansion rates. Additionally, when rigid structural foams, reinforcing materials, or other adhesives are used to bond braces directly to a panel, local plastic deformations may occur as a result of the different thermal expansion rates or variances in the applied bonding material, causing a permanent visible deformation on the outside of the panel.
FR 2897335 discloses a mastic bead that is expandable. Such mastic materials tends to be very sticky, and are also typically applied in a paste form or are otherwise viscous in nature. Accordingly, a mastic material is generally difficult to apply, and at a minimum may require specialized machinery for applying the mastic material accurately and in the appropriate amount. Additionally, the material properties of the expanded mastic materials may cause similar problems noted above in regard to other known bonding materials, which may cause a permanent visible deformation on the outside of the panel due in part to the rigidity of the expanded material.
Accordingly, there is a need for an improved reinforced panel or support structure that provides adequate stiffness to a panel while minimizing the above difficulties.